The present invention relates to semiconductor detection modules in which semiconductor radiation detection elements can be replaced, and to a radiation detection apparatus or a radiological imaging apparatus or a nuclear medicine diagnostic apparatus, such as a single photon emission computer tomography apparatus (referred as a SPECT apparatus hereinafter) or a positron emission tomography apparatus (referred to as a PET apparatus hereinafter), using the semiconductor detection modules.
As a radiation detection apparatus for detecting radiation such as gamma rays, one using a NaI scintillator has conventionally been known.
FIG. 5 is a conceptual cross-sectional diagram showing an internal construction of a gamma camera 100 having a NaI scintillator 101.
As FIG. 5 shows, in the gamma camera 100 having the NaI scintillator 101, which is a kind of a nuclear medicine diagnostic apparatus, gamma rays 109 which are a form of radiation enter the NaI scintillator 101 with limited angles through though-holes 106s that are formed in a collimator 106. Then, the gamma rays interact with a NaI crystal of the NaI scintillator 101 to emit scintillation light. The light reaches a photomultiplier 103 via a light guide 102 to become an electric signal. The electrical signal is wave-shaped by a measurement circuit 104 that is attached to a measurement circuit fixing board 105, and is outputted from an output connector 107 to an external data collection system as shown by a white arrow.
These NaI scintillator 101, light guide 102, photomultiplier 103, measurement circuit 104, measurement circuit fixing board 105, and the like are all housed in a light blocking shield case 108. Electromagnetic waves other than outside radiation are blocked by the light blocking shield case 108.
Typically, the gamma camera using the scintillator has a structure in which the large photomultiplier 103, also referred to as a photomul, is disposed behind a crystal such as a sheet of large NaI, as shown in FIG. 5. Therefore, an intrinsic position resolution relative to a target object stays at approximately 4 mm.
In addition, the scintillator 101 performs detection after a process of multi-stage conversions; from radiation to visible light and from visible light to electrons. Therefore, the scintillator 101 has a problem that loss or the like arises during an intermediate stage and causes the scintillator 101 to have poor energy resolution. Therefore, it is impossible to separate scattered radiation that has mixed in during the intermediate stage, and the scattered radiation becomes noise. This deteriorates the SN ratio of a signal that represents information on a true position from which the gamma rays 109 are emitted, resulting in the deterioration of the image quality and an increase in the time required for picking up images.
Some PET apparatuses have a position resolution of 5 to 6 mm, while some high-end PET apparatuses have a position resolution of on the order of 4 mm. However, they also have a problem caused by the SN ratio.
Radiation detection apparatuses for detecting radiation based on a principle different from that of such a scintillator include a semiconductor detection apparatus 200 comprising semiconductor radiation detection elements 201, . . . that use a semiconductor material such as CdTe (cadmium telluride), TlBr (thallium bromide), and GaAs (gallium arsenide) (see FIG. 6). FIG. 6 is a diagram showing an example of an internal structure of a coupled part when a radiation detection apparatus is constructed by combining two semiconductor detection modules that are used for the nuclear medicine diagnostic apparatus or the like.
In the semiconductor detection apparatus 200, the semiconductor radiation detection elements 201, 202, 209, . . . directly convert an electric charge, which is generated by an interaction between the radiation and the semiconductor material of the semiconductor radiation detection elements 201, 202, 209, . . . into an electric signal. Thus, they perform conversion into an electric signal with efficiency higher than that of a scintillator, and have an excellent energy resolution. Therefore, the semiconductor detection apparatus 200 is now attracting attention. Here, having the excellent energy resolution means improvement of the SN ratio of the radiation detection signal indicating true position information, that is, improvement of detection accuracy. Moreover, various effects can be expected, such as improvement of contrast of an image and a reduction in the time required for picking up images. The two-dimensional disposition of the semiconductor radiation detection elements 201, 201, 209, . . . on a substrate allows detection of the position of a radiation emission source (see paragraphs 0120 and 0121, and FIG. 14 of JP-A-2000-56021).